1. Field of the Invention
The exemplary embodiments generally relate to a corner crackstop and a method of making the corner crackstop in each of the four corners of an integrated circuit (IC) chip, in which the corner crackstop differs structurally from a portion of the crackstop disposed along the sides of the IC chip. More specifically, each corner crackstop includes a plurality of layers disposed between a silicon layer and a final passivation layer of the IC chip. The plurality of layers of the corner crackstop include crackstop elements, each comprising a metal cap centered over a via bar. Yet more specifically, the plurality of layers of the corner crackstop is chamfered to deflect crack ingress forces by each corner crackstop.
2. Description of Related Art
In manufacturing semiconductor devices, a number of integrated circuits (ICs) are simultaneously prepared on a semiconductor wafer by conventional photolithography techniques. The ICs, which are rectangular in shape, are disposed in a grid pattern on the semiconductor wafer. Each of the four sides of each individual IC is adjacent to a dicing lane. The individual ICs are singulated by dicing the wafer along the dicing lanes with either a saw or laser to form IC chips or dies.
An individual IC chip includes an active region that comprises active and passive electrical devices, which provide the IC's functionality, and a perimeter boundary region that is adjacent to the dicing lanes. The active and passive electrical devices are formed within the semiconductor layer of the active region, which is located behind a crackstop that separates the active region from the perimeter boundary region. The IC chip, including both the active region and the perimeter boundary region, is covered by a plurality of metallization layers, each of the metallization layers including a patterned intermetallic dielectric layer that includes vias and an overlaying patterned metal layer. Within the active region, each of the plurality of metallization layers includes electrical contacts, formed within the vias that contact the overlying patterned metal layer. The patterned metal layer forms interconnect with the electrical contacts to the underlying active and passive electrical devices of the semiconductor layer.
Upon dicing, the IC chip is subject to crack ingress forces along its sides and greater crack ingress forces at the corners. Conventionally, a crackstop is formed parallel to the rectangular perimeter of the IC chip to prevent the crack ingress forces from delaminating or cracking the electrical devices and the metallization layers of the active region. A crackstop includes a plurality of layers formed on the silicon layer of the perimeter boundary region, each layer being formed by processes identical to those used in forming the metallization layers of the active region of the IC chip.
FIG. 1 illustrates a top view, in the x-y plane, of a conventional crackstop 150, disposed on an IC chip 110, in which an overlying final passivation layer is removed to view crackstop 150. The crackstop 150 includes portions that are beveled in the corner regions of the IC chip 110 to provide greater protection to the active region 160 from the greater ingress crack forces at the corners. The portions of the crackstop 150 that parallel the sides of the IC chip 110 and those portions of the crackstop 150 that are beveled in the corner regions include the same plurality of layers and the same structural elements within each layer.
FIG. 2 illustrates, in greater detail, a top view of corner region A (dotted lines) of FIG. 1. Referring to FIG. 2, a beveled portion of the crackstop 150 defines a hypotenuse, H, in the x-y plane, of a triangular area that is further defined by two right-angled sides (dotted lines), which extend from those portions of the crackstop 150 that parallel the sides of the IC chip 110. This triangular area, which forms the perimeter boundary region of each of the four corner regions of IC chip 110, provides greater protection to the active region 160 from the greater ingress crack forces generated at the corners, when compared to a crackstop that parallels the rectangular perimeter of an IC chip. In FIG. 2, a construction line, C-C′, in the x-y plane, extends from a corner of the IC chip 110 to cross the beveled portion of the crackstop 150 at a right angle.
Referring to FIGS. 3A and 3B, FIG. 3A illustrates a cross-section of crackstop 150 in a plane defined by the z-axis and construction line C-C′, as viewed along the hypotenuse, H, shown in FIG. 2, while FIG. 3B illustrates another cross-section of crackstop 150 in a plane defined by the z-axis and the hypotenuse, H, as viewed from C of the construction line C-C′, i.e., from the corner of the IC chip 110 toward the center of the IC chip 110. Crackstop 150 is formed on the silicon layer 315 of the IC chip 110 by, for example, four layers, 301-304, each layer comprising crackstop elements that include a metal cap 320 centered above a via bar 310. The via bar 320 differs from a conventional contacting cylindrical via by having a length, oriented along H, that exceeds its width.
Processes identical to those that form the metallization layers of the active region 160 of the IC chip 110 simultaneously form each layer of crackstop 150. Each metallization layer of the active region 160 comprises a patterned metal layer, which corresponds to the metal cap 320 of a layer of crackstop 150, and electrical contacts, formed within the intermetallic dielectric layer, which correspond to the via bar 320. These processes of simultaneously forming the metallization layers of the active region 160 and the layers of crackstop 150 include: deposition of an intermetallic dielectric on a silicon substrate in the active region 160 and the perimeter boundary region; patterning the intermetallic dielectric to form vias in the active region 160 and via bars in the perimeter boundary region; filling the vias with metal to form electrical contacts in the active region 160 and the via bars with metal to form part of a crackstop element in the perimeter boundary region; and depositing and patterning a metal layer over the electrical contacts and intermetallic dielectric to form interconnects between the electrical contacts in the active region 160 and over the via bars and intermetallic dielectric to form overlying metal caps on the via bars in the perimeter boundary region.
In contrast to the electrical contacts and the patterned metal interconnects of the active region 160, the metal caps 330 and via bars 320 of the crackstop 150 do not electrically contact any of the active or passive electrical devices in the active region 160 of the IC chip 110. Instead, the metal caps 330 and via bars 320 of the crackstop 150 perform a mechanical function of preventing the ingress of crack forces to the active region 160 located behind crackstop 150 of IC chip 110.
Referring to FIG. 3B, each metal cap 330 and via bar 320 of the beveled portion of the crackstop 150 extends the length of the hypotenuse, H, and joins the metal caps and via bars, at an approximately 45° angle, of the metal cap and via bar structures of those portions of the crackstop 150, which parallel the sides of the IC chip 110. Thus, the vertically aligned crackstop elements of the beveled portions of the crackstop 150, i.e., a metal cap 330 centered over a via bar 320, are the same as those vertically aligned crackstop elements, i.e., a metal cap centered over a via bar, of those portions of the crackstop 150, which are parallel to the sides of the IC chip 110. Viewed from C of the C-C′ construction line shown in FIG. 2, the metal caps 330 and via bars 320 of the layers of the beveled portion of the crackstop 150, illustrated in FIG. 3B, form a vertical metal “wall”, between the silicon layer 305 and the final passivation layer 335 that prevents the ingress of crack forces in the corner region. Those areas (dotted lines) to the right and left of the metal caps 330 and the via bars 320 of FIG. 3B, represent the same metal cap and via bar structures of those portions of the crackstop 150, which parallel the sides of the IC chip 110. FIG. 3A shows that this vertical metal “wall” comprises a plurality of layers, each layer including crackstop elements of a metal cap 330 centered above a via bar 320, where the metal caps 330 and via bars 320 are vertically aligned among all of the layers 301-304.
Although the top view of FIG. 2 shows the beveled portion of conventional crackstop 150 comprising a rectilinear structure oriented along the angle of the hypotenuse, H, an outward-facing surface of the rectilinear angled structure can be “broken up” into a zigzag pattern 402 of structural elements, as shown in FIG. 4A. It is thought that the zigzag pattern 402 helps to “break up” the ingress of crack forces into the corner region. The zigzag pattern 402 can be extended to those portions of the crackstop, which are parallel to the sides of the IC chip. Referring to FIG. 4A, individual crackstop elements, each including a metal cap centered over a via bar that is oriented parallel to a beveled portion of the corner crackstop, can form zigzag pattern 402. Alternatively, a semiconductor manufacturing process may approximate a rectilinear angled structure by forming a right-angled zigzag pattern of crackstop elements along the x-y axes of the IC chip, as shown in FIG. 4B, to form an outward-facing surface of the corner crackstop. Referring to FIG. 4B, individual rectangular corner crackstop elements 430, each including a metal cap centered over a via bar that is oriented along the x-y axes of the IC chip, can form right-angled zigzag pattern 404, which approximates the rectilinear beveled portion of a corner crackstop. Again, it is thought that the zigzag pattern 404 helps to “break up” the ingress of crack forces into the corner region.
There remains a need to maximize crack stopping robustness without decreasing the active region of an IC chip, which is protected by a conventional crackstop having beveled portions in the corner regions, where the same vertically aligned crackstop elements are formed in the beveled portions of the conventional crackstop and in those portions of the conventional crackstop that are parallel to the sides of the IC chip.